Halogen-containing flame retardants

The oxidation that occurs in the vapour phase is a free radical process and additives that can trap radicals such as H , O, HO2 and OH may be useful as flame retardants. Halogen-containing compounds are an example of particularly good radical scavengers and thus halogenated organic compounds find extensive use in flame retarded compound formulations. 

Flame Retardants. Bromine compounds make up an important segment of the market for flame retardants used in polymers. Additive flame retardants are added to polymers during processing reactive flame retardants react chemically to become part of the polymer chain itself In addition to the compounds listed in Table 3, a number of proprietary mixtures and phosphorus—bromine-containing flame retardants are also sold (see Flame retardants, HALOGENATED, FLAME RETARDANTS). 

Any post-consumer plastic stream will contain some halogens in the form of polyvinyl chloride, polyvinylidene chloride, brominated flame retardants, halogenated additives, food waste, or salt. Therefore, two issues must be considered. First, the gas stream resulting from the depolymerization of plastics must be scrubbed to remove any halogenated gases to satisfy emissions controls. Second, halogens in the liquid product must be minimized to increase its value and marketability. Therefore the Conrad process has been developed. It is a robust process unit that can accommodate a variable feedstream and produce a consistent product, free of nonhydrocarbon impurities by low feed preparation costs. 

Molybdenum and zine eontaining compounds have been used as flame and smoke suppressants for a variety of polymers. These metal containing species normally act to assist the build-up of char on the pol mier surface. This ehar is presumed to be the main method of flame retardancy. Halogenated systems form a large proportion of the market for molybdenum and zinc compounds. 

The producers of computers, printers, monitors, copiers and keyboards would all like to utilise environmental labels like the Blauer Angel (Blue Angel) or the TC099 to their equipment. A feature common to all the award guidelines is that they largely exclude the use of plastics incorporating flame retardants that contain halogen. 

Grades (such as MagShield from Martin Marietta) exhibit low toxicity (LD50 (oral/rat) >5000 mg kg ) and are non-corrosive compared with flame-retardant systems containing halogen or phosphorus. 

Z. Z. Wang, B. J. Qu, W. C. Fan, and P. Huang, Combustion characteristics of halogen-free flame-retarded polyethylene containing magnesium hydroxide and some synergists. Journal of Applied Polymer Science, 81 (2001), 206-14. 

Subsequent hydrolysis produces P2O3 or H3PO4. When triphenyl phosphine oxide is used, P2-, PO-, P02-, and small amounts of P- and HPO- are found in zone 3 of the flame and can react with active radicals directly in that zone [28]. The synergetic effect of flame-retardant combinations containing phosphorus and a halogen may still be increased by the reaction between degradation products that are formed in the pyrolysis zone [29]. The HCl formed by the decomposition of the halide... 

Other flame-retardant adhesives contain vi-nylidene chloride latexes, halogenated epoxies, or additives such as diammonium phosphate or ammonium sulfamate. The epoxy resin derived from tetrabromo- or tetrachlorobisphenol A is used in special aircraft adhesives. 

In general, the acute toxicity of halogenated flame retardants is quite low. Tables 11—14 contain acute toxicity information from various manufacturers material safety data sheets (MSDS) for some of the flame retardants and intermediates Hsted in the previous tables. The latest MSDS should always be requested from the suppHer in order to be assured of having up-to-date information about the toxicity of the products as well as recommendations regarding safe handling. 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

---